1,3,5-Trimethylbenzene

1,3,5-Trimethylbenzene (mesitylene; CAS 108-67-8) is a symmetric aromatic hydrocarbon found as a natural constituent of heavy aromatic petroleum naphtha fractions and crude oil. It is a colorless, flammable liquid with a characteristic petroleum-aromatic odor. At the 2–4% concentrations where it appears in diesel fuel treatments alongside the heavier aromatic naphtha carrier, it contributes to the product's total VOC load and the aromatic solvent inhalation profile during the pour scenario.

The compound shares the same general hazard profile as its trimethylbenzene isomers (1,2,4- and 1,2,3-TMB): flammable, skin and eye irritant, respiratory irritant at elevated concentrations, and harmful if inhaled in vapor form. It carries H411 chronic aquatic toxicity and is not readily biodegradable, making it an environmental concern when released to waterways.

1,3,5-Trimethylbenzene is not on California Proposition 65, is not classified as a carcinogen or asthmagen, and is not a PFAS or endocrine disruptor. Its primary role in diesel treatment formulations is as an incidental constituent of the aromatic naphtha carrier, not as a functional active ingredient.